Recommendation regarding zsh compinit

nh2 commented 1 year ago

Hi, a hit an issue with zsh that starting a new shell (by opening a new terminal, typing zsh, or benchmarking with command time zsh -i -l -c ':') took ~300 ms, causing a noticeable, annoying delay.

Using zprof (e.g. as described here) showed that compinit and compaudit took > 85% of that time, and that they were called repeatedly (3 times for me). Both are related to zsh's completion system.

After a bit of reasearch, e.g. mainly https://dev.to/djmoch/zsh-compinit--rtfm-47kg, I learned that during zsh startup:

You need to initialise the zsh completion system once by calling compinit
By default (when not calling it with -C), it also creates a cache file .zcompdump; this takes extra long
Any time you add some completions afterwards during zsh startup (e.g. via home-manager's plugins for other shell-integrating software like atuin, fzf, or skim) which modifies the fpath (if I understood it right), zsh automatitically has to re-run compinit.

Here is my concrete setup:

Using global NixOS config in /etc/nixos/configuration.nix (where I load the grml zsh config)
A bit of extra user-specific config in home-manager's home.nix

Because of that, I get compinit calls in:

GRML's own config that I include (and which apparently cannot easily be turned off)
the global NixOS zsh config (NixOS module setting, code that does the call)
home-manager zsh module (module setting, code that does the call)

In the latter, it seems home-manager already knows about the problem, because there's a comment:

https://github.com/nix-community/home-manager/blob/78ceec68f29ed56d6118617e9f0f588bf164067f/modules/programs/zsh.nix#L519-L524

        # Oh-My-Zsh/Prezto calls compinit during initialization,
        # calling it twice causes slight start up slowdown
        # as all $fpath entries will be traversed again.

My issue request:

home-manager should give some advice what to do in such situations, to minimise compinit/startup time e.g. when mixed NixOS/home-manager zsh configs are in use.

nh2 commented 1 year ago

I currently came up with the following workaround:

In /etc/nixos/configuration.nix:

  # zsh
  programs.zsh.enable = true;
  programs.zsh.interactiveShellInit = ''
    # Enable the below for profiling zsh's startup speed.
    # Once enabled, get numbers using:
    #     zsh -i -l -c 'zprof'
    #zmodload zsh/zprof

    # Disable `compaudit` being invoked from GRML cominit call.
    # See: https://grml.org/zsh/grmlzshrc.html
    # This speeds up shell loading.
    zstyle ':grml:completion:compinit' arguments -C

    # Load grml's zshrc.
    # Note that loading grml's zshrc here will override NixOS settings such as
    # `programs.zsh.histSize`, so they will have to be set again below.
    source ${pkgs.grml-zsh-config}/etc/zsh/zshrc

    # From https://htr3n.github.io/2018/07/faster-zsh/
    # Theoretically it should not be needed (as described on https://dev.to/djmoch/zsh-compinit--rtfm-47kg)
    # but I couldn't figure out how to make the GRML zshrc do only a single compinit
    # without compaudit but generating .zcompdump (I use `-C` for
    # `:grml:completion:compinit` above to avoid compaudit but that also skips
    # generating `.zcompdump` apparently).
    # Snippet based on https://gist.github.com/ctechols/ca1035271ad134841284
    autoload -Uz compinit
    if [[ -n ${ZDOTDIR:-$HOME}/.zcompdump(#qN.mh+24) ]]; then
      compinit
    else
      # We don't do `compinit -C` here because the GRML zshrc already did it above.
    fi
  '';
  programs.zsh.promptInit = ""; # otherwise it'll override the grml prompt

  # Speed up zsh start by running compinit manually (see config above).
  programs.zsh.enableGlobalCompInit = false;

In home.nix:

    zsh = {
      enable = true;
      # Using GRML zshrc in /etc/nixos/configuration.nix currently
      # instead of `oh-my-zsh` because so far it cannot properly show
      # git rebases in the prompt, which I care a lot about.

      # My global NixOS config does `compinit` already.
      # Disabling it in my user's `.zshrc` because calling it multiple
      # times causes startup delay, see:
      #     https://github.com/nix-community/home-manager/blob/990b82ecd31f6372bc4c3f39a9171961bc370a22/modules/programs/zsh.nix#L518-L524
      enableCompletion = false;
    };

So in summary, I

tell both NixOS's and home-manager's zsh module to not call compinit, because GRML does it already
I tell the GRML call to pass -C so that it doesn't run compaudit (which I try to avoid overall)
I use the approach that many blogs link to (https://gist.github.com/ctechols/ca1035271ad134841284) to run full compinit (without -C) only once per day, instead of at each zsh startup.

This works, but I am not sure if it is optimal, and it also means that if compaudit prints any warnings, I only get the chance to see them once per day (which I guess is fine for me).

stale[bot] commented 1 year ago

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dongho-jung commented 1 year ago

thanks, you saved my day indeed

EDIT. I found that when I use zplug, it compinit on behalf of me so I could get rid of compinit things from my nixes

stale[bot] commented 11 months ago